The present invention relates to a method of producing a composite magnetic sheet formed by mixing soft magnetic powder into an organic binding agent and, in particular, to a method of producing a composite magnetic sheet for use in an electromagnetic interference suppressing body.
An electromagnetic interference suppressing body is used for suppressing electromagnetic interference caused by interference of undesired electromagnetic waves.
Conventionally, for blocking invasion of the external undesired electromagnetic waves into an electronic device, shielding of the electronic device by a conductor has been carried out. However, since the blocking of the electromagnetic waves by the conductor aims to reflect the electromagnetic waves, radiant waves from a certain component within the electronic device may be reflected to adversely affect other components in the same electronic device as secondary noise. Particularly, following reduction in size and increase in working frequency of electronic devices in recent years, problems of the interference due to the external electromagnetic waves and the secondary noise due to the internal electromagnetic waves are serious.
JP-A-7-212079 discloses a composite magnetic body which can suppress interference of undesired electromagnetic waves utilizing absorption of high-frequency waves due to a complex permeability of a soft magnetic body of a certain kind. This composite magnetic body is constituted of a composite magnetic sheet formed by mixing soft magnetic powder into an organic binding agent.
The sheet of the composite magnetic body may be used as it is. On the other hand, by forming a structure stacked with a conductive sheet, the coming electromagnetic waves are absorbed by the composite magnetic sheet and the electromagnetic waves passing through the composite magnetic sheet are reflected by the conductive sheet into the composite magnetic sheet, so as to suppress the interference of the undesired electromagnetic waves.
Such an electromagnetic interference suppressing body is disposed, for example, on the surface of an electronic device or around an electronic component in the electronic device which is liable to suffer an influence of the external electromagnetic waves. Alternatively, it is used so as to be disposed between two printed circuit boards each mounted thereon with electronic components and confronting each other with a space therebetween.
Incidentally, the foregoing composite magnetic sheet has been produced by hot pressing a kneaded slurry material in the form of soft magnetic powder and an organic binding agent suspended and dispersed in an organic solvent.
There is a drawback that when the composite magnetic sheet are produced by the hot pressing, entrainment of the air into the composite magnetic sheets can not be avoided so that the yield of the composite magnetic sheets is bad.
Further, since the producing method based on the hot pressing is a batch process, it is unsuitable for the mass production.
On the other hand, an absorption capacity of undesired electromagnetic waves of the composite magnetic body is determined by a thickness thereof assuming that a material to be used is the same.
Therefore, an object of the present invention is to provide a producing method which can accomplish the mass production of composite magnetic sheets of a required thickness.
Another object of the present invention is to provide a method of producing a composite magnetic sheet which can obtain a high-quality composite magnetic sheet with less entrained air.
Further, another object of the present invention is to provide a method of producing a composite magnetic sheet which, in view of the shape thereof, reduces reflected components and transmitting components and improves the absorption rate of electromagnetic waves.
Another object of the present invention is to provide a method of producing an electromagnetic interference suppressing sheet having a stacked structure of composite magnetic sheets and a conductor layer without readiness of mechanical exfoliation.
According to the present invention, as recited in claim 1, there is obtained a method of producing a composite magnetic sheet characterized by a step of preparing an atomized mixture of soft magnetic powder and an organic binding agent; and a step of rolling the foregoing atomized mixture by mutually confronting two rolls to obtain the foregoing composite magnetic sheet.
Modifications and carrying-out manners of this method are recited in dependent claims 2 and 15.
Further, as recited in claim 16, an electromagentic interference suppressing body using the composite magnetic sheets produced by the foregoing method of the present invention can be produced as a stacked sheet by sandwiching a conductive sheet having a plurality of holes between the two composite magnetic sheets and attaching these sheets under pressure by mutually confronting two rolls.
Carrying-out manners and modifications of the method of producing the electromagnetic interference suppressing body of claim 16 are recited in dependent claims 17 to 19.